GHSA-grvv-h2f9-7v9c is a medium-severity (CVSS 5) CWE-863 vulnerability in github.com/matrix-org/dendrite. A fix is available for github.com/matrix-org/dendrite — see the affected versions and patch details below.
gomatrixserverlib and Dendrite vulnerable to incorrect parsing of the event default power level in event auth
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-grvv-h2f9-7v9c.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-grvv-h2f9-7v9c plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,238 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/matrix-org/dendrite🐹github.com/matrix-org/gomatrixserverlibReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Impact
The power level parsing within gomatrixserverlib was failing to parse the "events_default" key of the m.room.power_levels event, defaulting the event default power level to zero in all cases.
In rooms where the "events_default" power level had been changed, this could result in events either being incorrectly authorised or rejected by Dendrite servers.
Patches
gomatrixserverlib contains a fix as of commit 723fd49 and Dendrite 0.9.3 has been updated accordingly.
Workarounds
Matrix rooms where the "events_default" power level has not been changed from the default of zero are not vulnerable.
For more information
If you have any questions or comments about this advisory, e-mail us at [email protected].
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/matrix-org/dendrite | all versions | 0.9.3go get github.com/matrix-org/dendrite@v0.9.3 |
| 🐹Go | github.com/matrix-org/gomatrixserverlib | all versions | 0.0.0-20220815091947-723fd495dde8go get github.com/matrix-org/gomatrixserverlib@v0.0.0-20220815091947-723fd495dde8 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/matrix-org/dendrite, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/matrix-org/dendrite to 0.9.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-grvv-h2f9-7v9c is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-grvv-h2f9-7v9c can be triaged on real exposure rather than presence alone.
Tailored to GHSA-grvv-h2f9-7v9c. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-grvv-h2f9-7v9c in your dependencies?
O3 Security finds GHSA-grvv-h2f9-7v9c across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.